Dielectric heating/drying systems are known and are currently in use or have been proposed for use in agriculture, polymer manufacture, pharmaceuticals, bulk powder, food processing, wood products, and other industries. One of the key industries using these dielectric heating/drying systems is the wood products industry and the present invention will be described particularly with respect to the wood products industry although the invention, with suitable modifications where required, may be applied in the other industries in which dielectric heating/drying is to be performed.
In dielectric drying systems (particularly those for drying wood of the type described in U.S. Pat. No. 3,986,268 issued Oct. 19, 1976 to Koppelman), it is conventional practice for the lumber to be moved into the drying chamber, at least one power electrode that will emit electromagnetic energy and a grounding electrode to complete the circuit are positioned near or in contact with the load. After the load has been positioned in the kiln these power and grounding electrodes are connected electrically to the source and ground respectively and then the kiln chamber may be closed and the drying process may commenced. This original material handling system, though adequate for many applications, does not lend itself to rapid loading and unloading nor does it facilitate automatic handling or operation of the kiln.
As above indicated, this original method requires manually connecting the radio-frequency (RF) generator to one or more electrodes before the drying cycle may be started and disconnecting the RF generator from the electrode(s) after drying and before the load may be removed from the kiln. This loading and unloading, connecting and disconnecting etc., necessitates the use of professionally trained personnel both for safety and operating procedures to better ensure there are no major problems or accidents. These limitations imposed by the use of the original type of connecting straps have given the process of dielectric drying a reputation of being non-robust in that it requires flimsy attachments which lead those in the lumber industry to imply that the technique is still in the research and experimental stage and has not yet been developed for commercial industrial purposes. In this original design, wide conductive straps (generally made of copper or aluminum with aluminum being the preferred material in most applications) are typically used. There are two further weaknesses with this approach. Firstly (and as often encountered in these types of systems), the sharp edges of these conductive straps create a high risk of catastrophic arcing due to a phenomenon known as electric field breakdown. (1/32" thick straps will at best have radiused edges of 1/64" but typically, a much smaller radius.) Secondly, it is preferred that all connection cables within a process of this type have low inductance (meaning wide thickness and short length if conductive straps are used). Therefore, if such conventional electrode straps are used and remain connected to a movable electrode, it is clear that longer (and flexible) straps will be required. Longer straps increase the inductance of the straps creating higher voltage drops across the straps resulting in higher risks of catastrophic arcing due to electric field breakdown.